Note: Descriptions are shown in the official language in which they were submitted.
DESCRIPTION
IMPROVEMENTS REI~TING 10 SMOKE ~ILTERS
mis invention relates to smoke filters for use
with smoking articles, cigarettes for example.
A number of proposals have heretofore been made
for cigarette filters having provision for the ingress
of ventilation air into ducts exten~; ng at the periphery
of the filter to the mouth end thereof and serving to
convey the air to the smoker's mouth without any, or
substantially any, mixing of the air within the filter
with tobacco smoke drawn through the filter. Such mode
of filter ventilation may be referred to as "segregated
peripheral ventilation".
It has been claimed for segregated peripheral
ventilation filters that they enhanc~ the quality of the
tobacco smoke as perceived by the smoker.
~he present invention provides a smoke filter
comprising a rod-like plug of filtration material and
having at least one airflow duct extending along said
plug between a first end of the duct open at the mouth
end of said plug and a second end open at the periphery
of said plug, and wrapping means enwrapping said plug
and permitting the ingress of a first stream of ambient
air into said at least one airflow duct at a iocation
spaced from ~aid first end and permitting
the ingress of a second stream of
ambient air directly into the interior of said plug.
Preferably the ingress of said first stream of
ambient air into the duct is independent of the ingress
of a second stream of ambient air directly into the
interior of said plug. More preferably the at least
one airflow duct extends short of the other end of the
plug. Advantageously,the wrapping means, or an outer
layer thereof underlain by an air-permeable layer, is
provided with first and second ventila-tion perforations
for passage therethrough of the first and second streams
of air respectively~ Suitably, the second ventilation
perforations are located over a region of the periphery
of the filter plug longitudinally spaced from a region
thereof at which extend the airflow ducts. Conveniently,
the airflow duct is partly defined by a number of grooves
in the peripheral surface of the filter plug, as well as
by the wrapping means or inner layer thereof. The grooves
may extend parallel to the axis of the filter plug or may
be helical. There may be two sets of helical grooves of
opposite hand so that the grooves of one set intersect
the grooves of the other set.
The plug of filtration material may be other than
of unitary form. For example, it may comprise two
abutting sub-plugs, in which case one sub-plug may be
provided with grooves bounding the airflow duct~
By use of a filter according to the invention on a
4~1~
-- 3 --
cigarette, an unexpected improvement in the taste of
the mainstxeam ~moke is obtainable over that perceived
when a filter is employed of which the only mode of
ventilation is s~gregated peripheral ventilation.
In order that ~he invention may be clearly
understood and readily carried into effect, reference
will now ~e made, by way of example, to the accompanying
diagrammatic drawing,in which:-
FIGURE 1 shows a part view, in axial section, of a
filter-tipped cigarette,
FIGURE la shows a cross-sectional view of half of
the cigarette of Figure 1 taken along line A- A thereof,
FIGURE 2 shows a filter plug of an alternative
form from that of the cigarette of Figure 1, and
FIGURE 3 ~hows, partially in axial section, a
further alternative form of filter plug.
The cigarette of Figure 1 comprises a rod 1 of cut
tobacco enwrapped in cigarette paper 2, and a filter 3
comprising a self-sustaining filter plug 4 of fibrous
cellulose acetate filtration material. At the periphery
of the plug 4 there extend a series of grooves 5 - see
also Figure la. The grooves 5 open at the mouth end of
the plug 4 and extend parallel to the plug axis for about
half the length of the plug 4. A convenient method of
forming the grooves 5 is to subject the plug 4, or
~2~6æ
preferably a piece of filter rod material from which
several of the plugs 4 are to be cut, to a hot moulding
process such as, for example, that disclosed in United
Kingdom Patent Specification No. 1,507,765. Sealing of
the walls of the grooves 5 may be assured by the
application thereto of a sealant material,
polyethylene for instance.
Serving to secure the filter 3 to the cigarette
rod 1, 2 is a tipping 7. In the portions where it
overlies the grooves 5, the tipping 7 defines, together
with the walls of the grooves 5, airflow ducts 8. In
the tipping 7 are two rows of ventilation perforations
9 and 10. As is indicated in Figure 1, the row of
perforations 9 encircles the plug 4 at that portion
thereof at which the grooves 5 extend, the arrangement
being such that at least one of the perforations 9 is in
communication with each of the airflow ducts 83 The row
of perforations 10 encircles a portion of the plug 4
into which the grooves 5 do not extend~
The perforations g and 10 may, if desired, be
formed as micro-perforated regions of the tipping 7.
It is also possible for the tipping 7 to overlie a
plug wrapper of air-pervious quality in which case the
tipping serves as an outer layer in which the ventilation
perforations are provided.
A further alternative is for the tipping 7 to
overlis an imper~rious plug wrapper, in which case the
wrapper wculd bP provided with perforations in-register
with the perforations 10 in the tipping 7. Suitably
in such latter case the plug wrapper perforations would
be formed at the same time as the perforations 10,
mechanically or by laser drilling.
W~nen the cigarette of Figure 1 is smoked,
ambient air is drawn in through the perforations 10
directly into the filter plug 4 and mixes with tobacco
smoke passing through the latter. Ambient air is also
drawn in separately through the perforations 9 into the
airflow ducts ~ and passes along the ducts to the outlet
ends thereof unmixed, or substantially unmixed, with
smoke.
The filter plug shown in Figure 2 and generally
designated 11 is one which may be used in place of the
plug 4 of Figure 1. The plug 11 is provided with a
number of equally-spaced longitudinal grooves 12 which
open at the mouth end of the plug and extend therefrom
for substantially less than the fu]l length of the plug.
In a portion of the plug 11 clear of the longitudinal
grooves 12 the plug is provided with a deep annular
circumferential channel 13. The longitudinal grooves
12 and circumferential channel 13 may conveniently be
formed by a hot moulding process. ~hen the plug 11
is incorporated in a filter-tipFed cigarette, it is
~z~
enwrapped in a wrapping which is constructed to permit
the ingres~ of a first stream of air directly into
airflow ducts bounded by the walls of the longitudinal
grooves 12 and by the inwardly facing surface of the
wrapping, and a second, separate stream of air into
the circumferential channel 13. The second stream of
air directly enters the interior of the plug 11, mainly
through the downstre m side wall of the circumferential
channel 13~
If a tipping wrapper surrounding the filter plug 11
is provided with a row of perforations (like-the
perforations 9 of Figure 1) in register with the portion
of the plug in which the longitudinal grooves 12 extend
and if some intermediate ones of the perforations in that
row are disposed between the longitudinal grooves,
air may be prevented from entering the interior of the
plug 11 through such intermediate perforations by
applying a sealant to the peripheral surface of the
plug 11. Alternatively, the plug 11, or a piece of
filter rod of which the plug 11 initially formed part,
may be enwrapped in a non-permeable wrapper of
thermoplastic character prior to being hot-moulded to
provide the longitudinal grooves 12 and the
circumferential channel 13. In the latter
case the hot-moulding of the comparatively shallow
longitudinal grooves 12 leaves the non-permeable wrapper
substantially intact, whereas little or no remnant of
6~
the wrapper is observable in the deep circumferential
channel 13. Thus the walls of the longitudinal grooves
1~ are air-impermeable and at least the side walls of
the circumferential channel 13 are air-permeable.
Figure 3 shows another form of filter plug,
generally designated 14, which may be used in place of
the plug 4 of Figure 1. Plug 14 is provided with a
number of equally-spaced~ helical grooves 15 which
extend from the mouth end of the plug 14 and may be
formed by a hot-moulding process~ Plug 14 is also
provided, clear of the grooves 15, with a number of
holes 16 extending radially inwardly from the peripheral
surface of the plug. The holes 16 may be formed
mechanically or by a laser, formation of the holes
conveniently taking place after assembly of the plug
14 with a cigarette rod so that the step of forming
the holes 16 also results in the perforation of the
wrapper.
Although the above described filter plugs are of
a unitary nature, dual element plugs could be used, such
that a first element has grooves formed in it extending
from the mouth end of the first element, and the second
element has means for permitting the ingress of air into
the interior of the second element. The grooves in the
_ 25 first element could extend for the full length of the
first element. If such dual element plugs are wrapped
in respective plug wrappers, conveniently the wrapper
of the first element is air-impervious and that of the
second element is air-pervious.
The air/smokeregime issuing from each of the above
5 described filters, as far as it is due to the
segregated peripheral ventîlation, is modified by the
establishment within the filtex of an air/smoke flow
by virtue of the direct ventilation air flow into the
interior of the filter plug. This modification effect
results in an unexpected improvement in the taste of
the mainstream smoke~
The various perforations 9, 10 and 11 shown in the
drawing are not ~o scale and are exaggerated for ease
of illustration.
